[Mongoose]

If 9 is the one I'm thinking of, I only remember it from it being used in the final mission of Destiny of Peace.  It's a shame it wasn't used somewhere in the main campaign.  Though I'm not sure Good Luck would have been improved with it; just having the bare subspace ambiance lends a very creepy atmosphere.

[Vidmaster]

So, to come to a close, we pretty much have all the stuff we know about already, bar some mysterious tapes.

[Novachen]

Of unused voice files i can only tell about the unused, but voiced, debriefing stages in the Great War missions "Clash of the Titans" and "The Great Hunt" and "Tightening the Noose" of Operation Templar (well, that is technically FS2).

But these are only very obvious ones, because these debriefing stages are still in the missions. But no one mentioned them so far .